Thin-film catalysts are recently recognized as promising catalysts due to their reduced amount of materials and good catalytic activity, leading to low-cost and high-efficiency catalysts. A series of CuFeOx thin-film catalysts were prepared with different Fe contents using a one-step method as well as tested for the catalytic reduction of nitrous oxide (N₂O) in the presence of CH₄ at a high GHSV of 185 000 mL/(g∙h). The increase of iron strongly affects the dispersion and leads to the creation of a less-active segregated Fe₂O₃ phase, which was confirmed by XRD, EDX, and XPS outcomes. The results show that the synergistic properties between Cu and Fe, which affect the CuFeOx film catalysts in many aspects, such as the hollow-like texture, specific surface area, nano-crystallite size, the surface contents of Cu+, Fe³⁺, and oxygen species, the reductive strength and the strong active sites on the surface. Using DFT calculations, the adsorption and decomposition energy profiles of N₂O on the CuFeO₂ (012) surface model were explored. The surface Fe-site and hollow-site are active for N₂O decomposition, and the decomposition energy barriers on the Fe-site and the hollow-site are 1.02 eV and 1.25 eV respectively at 0 K. The strategy adopted here to tailor the activity through low-doping Fe-oxide catalysts could establish a promising way to improve the catalytic reduction of N₂O with CH₄.

Hydrogen is a type of clean energy which has the potential to replace the fossil energy for transportation, domestic and industrial applications. To expand the hydrogen production method and reduce the consumption of fossil energy, technologies of using renewable energy to generate hydrogen have been developed widely. Due to the advantages of widespread distribution and various hydrogen production methods, most of the research or review works focus on the solar and biomass energy hydrogen production systems. To achieve a comprehensive acknowledge on the development state of current renewable energy hydrogen production technology, a review on hydrogen production systems driven by solar, wind, biomass, geothermal, ocean and hydropower energy has been presented. The reaction process, energy efficiency, exergy efficiency, hydrogen production rate, economic and environmental performance of these systems have been evaluated. Based on the analysis of these different systems, the challenge and prospects of them are also analyzed.

The thermal stress-induced deformation issue of receiver is crucial to the performance and reliability of a parabolic-trough (PT) concentrating solar power (CSP) system with the promising direct steam generation (DSG) technology. The objective of the present study is to propose a new-type receiver with axially-hollow spiral deflector and optimize the geometric structure to solve the above issue. To this end, optical-flow-thermal multi-physics coupling models have been established for the preheating, boiling and superheating sections of a typical PT-DSG loop. The simulation results show that our proposed new-type receiver demonstrates outstanding comprehensive performance. It can minimize the circumferential temperature difference through the spiral deflector while lower the flow resistance cost through the axially hollow structure at the same time. As quantitatively evaluated by the temperature uniformity improvement (ε∆T) and the performance evaluation criteria (PEC), different designs are achieved based on different optimal schemes. When ε∆T is of primary importance, the optimal design with torsional ratio of 1 is achieved, with ε∆T=25.4%, 25.7%, 41.5% and PEC=0.486, 0.878, 0.596 corresponding to preheating, boiling, superheating sections, respectively. When PEC is of primary importance, the optimal design with torsional ratio of 6–6.5 is achieved, with PEC=0.950, 2.070, 0.993 and ε∆T=18.2%, 13.3%, 19.4% corresponding to preheating, boiling, superheating sections, respectively.

Infrared thermography, velocity and impingement pressure measurements alongside numerical modelling are used in this study to resolve (heated) surface temperature distributions of turbulent swirling impinging jets for two Reynolds numbers (Re=11 600 and 24 600). Whilst building upon earlier discoveries for this same geometry, this paper provides three new contributions: (1) identifying the role of impingement distance (H/D) as a deciding factor in the trade-off between more efficient heat transfer (at high swirl numbers) and achieving better substrate temperature uniformity (lower gradients), (2) developing correlations to predict Nusselt number for swirling and non-swirling cooling jets, and (3) predicting the underlying mixing field in these jets and its interplay with the thermal distributions resolved.
Results indicate substrate temperature uniformity varies based on H/D and swirl intensity (S) with a significant level of thermal non-uniformity occurring in near-field impingement (H/D=1) at stronger swirl (S=0.59 and 0.74). Four correlations describing the effects of S, Re, and H on the average heat transfer and stagnation heat transfer are developed and yield accuracies of 8% and 12%, respectively. Flow recirculation near the impingement surface is predicted at H/D=1 for stronger swirl jets which disappears at other substrate distances. The peak wall shear stress reduces and the flow impingement becomes radially wider at higher H/D and S. Stronger turbulence or eddy viscosity regions for non-swirling jets (S=0) are predicted in the shear layer and entrainment regions at  H/D=1, but such turbulence is confined to the impingement and wall jet regions for strongly swirling flows.

Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion. Interactions between fuel droplets (discrete phase) and fluid flow (continuous phase) have a considerable effect on liquid fuel evaporation. In this paper, both the single- and two-phase modeling of liquid fuel injection into a model evaporating chamber are presented. The influences of important issues such as turbulence models, coupling between gas phase and droplets, secondary break-up and air swirling on the current spray simulation are investigated. Accordingly, the shear stress transport turbulence model, Taylor analogy break-up and two-way coupling models are applied to simulate the two-phase flow. Atomization and spray of fuel droplets in hot air are modeled employing an Eulerian-Lagrangian approach. The current results show an acceptable agreement with the experiments. Adjacent the fuel atomizer, bigger droplets are detected near the spray edge and minor droplets are situated in the middle. With increasing the droplets axial position, the droplets diameter decreases with a finite slope. The smaller droplets have a deeper penetration, but their lifetime is smaller and they evaporate sooner. A linear relation between penetration and lifetime of smaller droplets is detected. Maximum droplet penetration and mean axial velocity of gas phase are observed for no air swirling case. The effect of variation of swirl number on the lifetime of droplets is almost negligible. By enhancing the swirl number, the uniformity of droplet size distribution is reduced and some large droplets are formed up in the domain.

Oxidation of acetylene (C2H2) has been investigated in a high-pressure jet-stirred reactor (HP-JSR) with equivalence ratios Φ=0.5, 1.0, 2.0 and 3.0 in the temperature range of 650 K–900 K at 1.2 MPa. 18 products and intermediates were analyzed qualitatively and quantitatively by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Generally, with Φ increasing, the production of intermediates increases significantly. CH₄, C₂H₄, C₂H₆, C₃H₆ and C3H8 were important intermediates, which were formed abundantly at Φ=3.0. Sufficient light hydrocarbon intermediates could be an important reason for significant formation of cyclopentadiene, benzene, toluene and styrene at Φ=3.0. A detailed kinetic mechanism consisting of 299 species and 2041 reactions has been developed with reasonable predictions against the present data and previous results obtained at 0.1 MPa. According to flux and sensitivity analysis, H and OH radicals play important roles in the consumption of C₂H₂. The combinations among light hydrocarbons and their free radicals are the main generation pathways of aromatics. C₃H₃, IC₄H₅ and AC3H5 are important precursors for the formation of aromatics. By comparing the results of atmospheric pressure and high pressure, it can be found that increasing the pressure is conducive to fuel consumption and aromatics generation.

Bunsen burner is a typical geometry for investigating the turbulence-flame interaction. In most experimental studies, only turbulence intensity u′ and integral scale l₀ are used to characterize the turbulent flow field, regardless of the perforation geometry of perforated plates. However, since the geometry influences the developing process and vortex broken, the plate geometry has to be considered when discussing the flame-turbulence interaction. In order to investigate conditions at the same l₀ and u′ using different geometries, large eddy simulation of CH₄/air flames with dynamic TF combustion model was performed. The model validation shows good agreement between Large Eddy Simulation (LES) and experimental results. In the non-reacting flows, the Vortex Stretching of circular-perforated plate condition is always larger than that of slot-perforated plate condition, which comes from the stresses in the flow fields to stretch the vorticity vector. In reacting flows, at the root of the flame, the Vortex Stretching plays a major role, and the total vorticity here of circular-perforated plate condition is still larger (53.8% and 300% larger than that of the slot-perforated plate at x/D=0 and x/D=2.5, respectively). More small-scale vortex in circular-perforated plate condition can affect and wrinkle the flame front to increase the Probability Density Function (PDF) at large curvatures. The 3D curvature distributions of both cases bias to negative values. The negative trend of curvatures at the instant flame front results from the Dilatation term. Also, the value of the Vortex Stretching and the Dilatation at the flame front of circular-perforated plate condition is obviously larger.

To better analyzing the temperature oscillation and the two-phase behavior inside a flat loop heat pipe, visual studies were conducted. Under the 20°C water cooling and horizontal orientation, the effects of the filling ratio and heat loads on the temperature oscillation were analyzed. Based on the experimental data, the results indicate that owing to the increased system pressure, the temperature oscillation decays as the filling ratio increases from 34% to 58%. Meanwhile, during the startup process, temperature oscillation tends to occur during the boiling and steady stages due to the more violent two-phase behavior, while the temperature curves are smooth during the slow evaporation stage. Moreover, as the heat load increases, the evaporation becomes more intense at the active zone of evaporator, leading to a faster startup process and a higher oscillation frequency. Besides, owing to the synergistic effect of two-phase flow in the compensation chamber caused by heat leak and subcooled liquid backflowing, a “breathing” oscillation behavior of the vapor-liquid interface is observed at the compensation chamber, which further leads to the unstable operation behavior of the loop heat pipe system.

Understanding the correlation between the physical features of composite components and thermal conductive pathway is beneficial to optimizing the overall heat-transfer performance. Herein, we conduct numerical simulation to investigate the thermal conductivity and heat flux distributions of alumina (Al₂O₃)-filled composites. The finite element model was verified by both experimental data and theoretical models. The crucial factors include the influence of the interface thermal resistance, the intrinsic thermal conductivity of the matrix and Al₂O₃ filler, and the size effect of Al₂O₃ fillers were investigated. For single Al₂O₃-filled composites, the results indicate that increasing the intrinsic thermal conductivity of the matrix is conductive to bridge the Al₂O₃ pathway along heat-transfer direction, but there are very limited contributions by enhancing the intrinsic thermal conductivity of Al₂O₃ filler, tuning the size of Al₂O₃ filler, and reducing the interface thermal resistance. After introducing the multiscale fillers, it is found that the high thermal conductivity can be achieved by regulating their size matching effect. At the optimal binary ratio of 70:30 (40 μm:15 μm) and ternary ratio of 55:35:10 (40 μm:15 μm:10 μm), the heat-conduction network presents the dominant skeleton of large-sized filler and the bridging branch of small-sized fillers features, which facilitates the formation of a complete and continuous thermal conductive network. This study gives a practical guidance for the thermal conductive design of Al₂O₃-filled composites.

Solar air heaters are at the centre of interest owing to their widespread use for various purposes. In the study, thermal performance analysis of a solar air heater that can be easily produced from daily waste materials is done. The system has a low-cost structure with both waste material use and a simple design. The proposed system is tested under different climatic conditions, and the energetic and the exergetic performance figures are obtained for the first time in literature. It is observed from the experimental tests that the results are stable and coherent as well as in good accordance with the similar attempts in literature with some cost reductions and performance improvements. Thermodynamic performance analyses indicate that the maximum energy efficiency of the system is about 21%, whereas the exergy efficiency is 1.8%. The energetic and exergetic outputs of the system are also determined to be 27 W and 3 W, respectively, which is promising.

The coal gasification fly ash (CGFA) is an industrial solid waste from coal gasification process and needs to be effectively disposed for environmental protection and resource utilization. To further clarify the feasibility of CGFA to prepare porous carbon materials, the physicochemical properties of ten kinds of CGFA from circulating fluidized bed (CFB) gasifiers were analyzed in detail. The results of proximate and ultimate analysis show that the CGFA is characterized with the features of near zero moisture content, low volatile content as low as 0.90%–9.76%, high carbon content in the range of 37.89%–81.62%, and ultrafine particle size (d₅₀=15.8–46.2 μm). The automatic specific surface area (SSA) and pore size analyzer were used to detect the pore structure, it is found that the pore structure of CGFA is relatively developed, and part of the CGFA has the basic conditions to be used directly as porous carbon materials. From SEM images, the microscopic morphology of the CGFA is significantly different, and they basically have the characteristics of loose and porous structure. XRD and Roman spectroscopy were used to characterize the carbon structure. The result shows that the CGFA contains abundant amorphous carbon structure, and thus the CGFA has a good reactivity and a potential to improve pore structure through further activation. Through thermal gravimetric analysis, it can be concluded that the order of reactivity of the CGFA under CO₂ atmosphere has a good correlation with the degree of metamorphism of the raw coal. The gasification reactivity of the CGFA is generally consistent with the change trend of micropores combined with the pore structure. According to the physicochemical properties, the CGFA has a good application prospect in the preparation of porous carbon materials.

The operating conditions greatly affect the electrolysis performance and temperature distribution of solid oxide electrolysis cells (SOECs). However, the temperature distribution in a cell is hard to determine by experiments due to the limitations of in-situ measurement methods. In this study, an electrochemical-flow-thermal coupling numerical cell model is established and verified by both current-voltage curves and electrochemical impedance spectroscopy (EIS) results. The electrolysis performance and temperature distribution under different working conditions are numerically analyzed, including operating temperature, steam and hydrogen partial pressures in the fuel gas, inlet flow rate and inlet temperature of fuel gas. The results show that the electrolysis performance improves with increasing operating temperature. Increasing steam partial pressure improves electrolysis performance and temperature distribution uniformity, but decreases steam conversion rate. An inappropriately low hydrogen partial pressure reduces the diffusion ability of fuel gas mixture and increases concentration impedance. Although increasing the flow rate of fuel gas improves electrolysis performance, it also reduces temperature distribution uniformity. A lower airflow rate benefits temperature distribution uniformity. The inlet temperature of fuel gas has little influence on electrolysis performance. In order to obtain a more uniform temperature distribution, it is more important to preheat the air than the fuel gas.  

Proton exchange membrane electrolysis cell (PEMEC) is one of the most promising methods to produce hydrogen at high purity and low power consumption. In this study, a three-dimensional non-isothermal model is used to simulate the cell performance of a typical PEMEC based on computational fluid dynamics (CFD) with the finite element method. Then, the model is used to investigate the distributions of current density, species concentration, and temperature at the membrane/catalyst (MEM/CL) interface. Also, the effects of operating conditions and design parameters on the polarization curve, specific electrical energy demand, and electrical cell efficiency are studied. The results show that the maximum distribution of current density, hydrogen concentration, oxygen concentration, and temperature occur beneath the core ribs and increase towards the channel outlet, while the maximum water concentration distribution happens under the channel and decreases towards the channel exit direction. The increase in gas diffusion layer (GDL) thickness reduces the uneven distribution of the contour at the MEM/CL interface. It is also found that increasing the operating temperature from 323 K to 363 K reduces the cell voltage and specific energy demand. The hydrogen ion diffusion degrades with increasing the cathode pressure, which increases the specific energy demand and reduces the electrical cell efficiency. Furthermore, increasing the thickness of the GDL and membrane rises the specific energy demand and lowers the electrical efficiency, but increasing GDL porosity reduces the specific electrical energy demand and improves the electrical cell efficiency; thus using a thin membrane and GDL is recommended.

Adding fins to a shell-and-tube phase change thermal storage is a simple and effective way to enhance the performance of the phase change heat storage unit, and the proper arrangement of the fins is essential to enhance the performance of the storage unit. To enhance the performance of the triplex-tube thermal storage unit, a novel V-shaped fin structure is presented in this paper. And the heat storage performance of the thermal storage system is studied by numerical simulation. Firstly, the performance of the triplex-tube thermal energy storage unit with different arrangements of V-shaped fins is investigated by a two-dimensional model and compared with the use of the traditional rectangular fin structure, and the optimal fin arrangement is derived. The results show that the V-shaped fins with the optimal arrangement can decrease the time for the PCM melting in the heat storage unit by 31.92% compared to the conventional rectangular fins. On this basis, the influence of fin angle and thickness on the heat storage unit was studied. Then, a three-dimensional model of the thermal storage unit was established. And the effect of the flow parameters (inlet temperature, inlet flow rate) of the heat transfer fluid (HTF) on its performance was discussed in detail. Finally, the stored energy analysis of the whole thermal storage unit is carried out.

Barocaloric refrigeration technology, one of the caloric-effect refrigeration technologies, is drawing more and more attention. Neopentyl glycol (NPG) was reported to have a giant barocaloric effect, making it a potential barocaloric material. However, the high solid-solid (S-S) phase transition temperature and low thermal conductivity hinder the application of NPG in barocaloric refrigeration. This work lowers the S-S phase transition temperature and improves the thermal conductivity of the NPG-based barocaloric material. An NPG/TMP (TMP: Trimethylolpropane) binary system with an S-S phase transition temperature of 283.15 K is prepared, in which the mass ratio of TMP is 20%. Graphene is then added to the binary system to enhance thermal conductivity, and the optimal mass ratio of graphene was determined to be 5%. The thermal conductivity of this composite is 0.4 W/(m·K), increased by 110% compared to the binary system. To predict the effect of enhanced thermal conductivity on the cold-extraction process of the barocaloric refrigeration cycle, a numerical model is developed. The results show that the cold-extraction time of the barocaloric refrigeration cycle utilizing the composite with 5% graphene as the refrigerant is shortened by 50% compared with that using the binary system.

The costs of conventional fuels are rising on a daily basis as a result of technical limits, a misallocation of resources between demand and supply, and a shortage of conventional fuel. The use of crude oil contributes to increased environmental contamination, and as a result, there is a pressing need to investigate alternate fuel sources for car applications. Biodiesel is a renewable fuel that is derived chemically by reacting with the sources of biodiesel. The present research is based on analyzing the effect of fish oil biodiesel-ethanol blend in variable compression engine for variable compression ratio (VCR). The processed fish oil was procured and subjected to a transesterification process to convert fatty acids into methyl esters. The obtained methyl esters (biodiesel) were blended with ethanol and diesel to obtain a ternary blend. The ternary blend was tested for its stability, and a stable blend was obtained and tested in VCR engines for its performance, combustion, and emission characteristics. In the second phase, experiments are conducted in the diesel engine by fueling the fish oil methyl ester and ethanol blended with diesel fuel in the concentration of 92.5 vol% of Diesel+7.5 vol% of Fish oil+1.25 vol% ethanol, 92.5 vol% of Diesel+7.5 vol% of Fish oil+5 vol% ethanol, 87.5 vol% of Diesel+12.5 vol% of Fish oil+1.25 vol% ethanol, 87.5 vol% of Diesel+12.5 vol% of Fish oil+5 vol% ethanol, 82.5 vol% of Diesel+17.5 vol% of Fish oil+1.25 vol% ethanol, 82.5 vol% of Diesel+17.5 vol% of Fish oil+ 5 vol% ethanol to find out the performance parameters and emissions. Because the alternative fuel performs better in terms of engine performance and pollution management, the percentage chosen is considered the best mix. The results showed that the use of a lower concentration of ethanol in the fish oil biodiesel blend improved the engine thermal efficiency by 5.23% at a higher compression ratio. Similarly, the engine operated with a higher compression ratio reduced the formation of HC and CO emissions, whereas the NO_x and CO₂ emissions increased with an increased proportion of biodiesel in diesel and ethanol blends.

Future high-power-density engines require high level of intake boost. However, the effects of boosting on mixing, combustion and emissions in existing studies are inconsistent. In this paper, the mixing, combustion and emission characteristics with intake pressures of 100–400 kPa at low, medium and high loads are studied. The results show that the increase of intake pressures is conducive to the enhancement of air entrainment, while the air utilization ratios are reduced, thus requiring injection pressure to be optimized to effectively improve the mixing. For the intake pressures of 100 kPa, the average chemical reaction path is low-temperature reaction route, while the path of higher intake pressures is dominated by high-temperature pyrolysis. For soot emissions, when the equivalence ratio is lower than 0.175, the oxygen in the cylinder is sufficient, so the effect of temperature decrease is more significant, which leads to the increase of soot emissions with the increase of intake pressures. Otherwise, the effect of increasing oxygen concentration is more significant, so soot decreases accordingly. When the peak of global temperature is lower than 1800 K, the effect of the increase of oxygen concentration is more dominant, so the NOx emission increases with the increase of intake pressures. Otherwise, the rule of NOx emissions is consistent with temperature changes.

Barocaloric refrigeration is regarded as one of the next-generation alternative refrigeration technology due to its environmental friendliness. In recent years, many researchers have been devoted to finding materials with colossal barocaloric effects, while neglecting the research on barocaloric refrigeration devices and thermodynamic cycles. Neopentyl glycol is regarded as one of the potential refrigerants for barocaloric refrigeration due to its giant isothermal entropy changes and relatively low operating pressure. To evaluate the performance of the barocaloric system using Neopentyl glycol, for the first time, this study establishes a thermodynamic cycle based on the metastable temperature-entropy diagram. The performance of the proposed system is investigated from the aspects of irreversibility, operating temperature range, and operating pressure, and optimized with finite-rate heat transfer. The guidance for the optimal design of the system is given by revealing the effect of the irreversibility in two isobaric processes. The results show that a COP of 8.8 can be achieved at a temperature span of 10 K when the system fully uses the phase transition region of Neopentyl glycol, while a COP of 3 can be achieved at a temperature span of 10 K when the system operates at room temperature. Furthermore, this study also shows that the system performance can be further improved through the modification of Neopentyl glycol, and some future development guidance is provided.

Post-combustion technology of circulating fluidized bed can largely reduce the emission of nitrogen oxides (NO_x) in the process of combustion and succeed in meeting the ultra-low NO_x standard for some fuels like Shenmu coal. Exploring the potential of synergistic control of the emissions of NO_x and sulphur dioxide (SO₂) under post-combustion technology has become a direction that needs further study. The experiments were conducted on a 0.1 MW (thermal) circulating fluidized bed (CFB) test platform, composed of a CFB main combustor and post-combustion chamber (PCC). The paper focuses on the effects of air distribution ratio and temperature in CFB and limestone addition on NO_x and SO₂ emissions. The experimental results showed that compared with traditional CFB combustion, post-combustion technology can reduce NO_x emission largely, but lead to a slight increase in SO₂ emission. The higher SO2 emissions at post-combustion can lead to less NO_x emission. With the decrease in λ_CFB, NOx emission first decreased and then increased; by contrast, SO₂ emission with λ_CFB first increased and then decreased. Under post-combustion, when λCFB was 0.9, NO_x emission was the minimum, while the SO₂ emission was the largest. Combustion temperature and limestone addition has less adverse effects on NO_x emission under post-combustion, compared with traditional CFB combustion. Limestone injection into the furnace is applicable under post-combustion, and the sulfur removal efficiency under post-combustion is very high, almost equivalent to that under traditional combustion.

Dry reforming of methane (DRM) process has attracted much attention in recent years for the direct conversion of CH₄ and CO₂ into high-value-added syngas. The key for DRM was to develop catalysts with high activity and stability. In this study, LaNiO₃ was prepared by the sol-gel, co-precipitation, and hydro-thermal methods to explore the influence of preparation methods on the catalyst structure and DRM reaction performance. The regeneration properties of the used LaNiO₃ catalysts were also investigated under steam, CO₂, and air atmospheres, respectively. The results showed that LaNiO₃ prepared by sol-gel method showed the best DRM performance at 750°C. The DRM performance of the samples prepared by hydro-thermal method was inhibited at 750°C due to the residual of Na+ ions during the preparation process. The regeneration tests showed that none of the three atmospheres could restore LaNiO₃ perovskite phase in the samples, but they could eliminate the carbon deposits in the samples during the DRM reaction, so the samples could maintain stable DRM performance at different cycling stages.